The disclosure relates generally to radio frequency (RF) antennas and more particularly to multi-band RF antennas in a multiple-input multiple-output (MIMO) antenna arrangement, which may be used in a distributed antenna system (DAS).
Wireless customers are increasingly demanding multimedia data services, such as streaming videos, on client devices. Concurrently, some wireless customers use their wireless devices in areas that are poorly served by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of DASs. DASs can be particularly useful when deployed inside buildings or other indoor environments where client devices may not otherwise be able to effectively receive RF signals from a wireless service provider. DASs include remote units configured to receive and transmit communications signals to client devices. The remote units can be provided as remote antenna units configured to wirelessly receive and transmit wireless communications signals in the antenna range of the remote antenna units.
As the wireless spectrum becomes more and more crowded, remote antenna units in DASs are increasingly relying on MIMO antennas to achieve higher data rates. One technique that enables the MIMO antennas to provide higher data rates is known as spatial multiplexing. In spatial multiplexing, a high-rate signal is split into multiple streams and provided to multiple antennas for simultaneous transmissions in the same RF band. Because multiple antennas are radiating electromagnetic energy at the same time in the same RF band, this poses a challenge in terms of antenna size and the achievable RF isolation between the multiple antennas. Space separation is a commonly used technique that can provide a desired level of RF isolation between the multiple antennas. In space separation, each of the multiple antennas is placed at a separation distance that is proportionally related to the wavelength of RF used by the multiple antennas. In other words, the separation distance is inversely determined by the radio frequency used by the multiple antennas. In this regard, the lower the radio frequency used by the multiple antennas, the longer the separation distance must be between each of the multiple antennas.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinence of any cited documents.